The present invention is generally directed to energy wheels and, more specifically, to minimum energy wheel configurations for energy storage and attitude control.
Today, most spacecraft that orbit the Earth contain attitude control, attitude reference and energy storage systems. In general, attitude control of the spacecraft has been accomplished by applying torques to the spacecraft through reaction wheel assemblies (RWAs) or control moment gyros (CMGs), while attitude reference has generally been provided by inertial sensors and devices that provide an absolute reference, such as sun and star sensors. Energy storage for the spacecraft has been performed by batteries that are charged by solar panels and energy wheels, which have performed both energy storage and attitude control.
In one known configuration 100 (FIG. 1), three pairs of energy wheels 102 and 104, 106 and 108, and 110 and 112 (FIG. 1) are implements within a spacecraft with each pair being located on a mutually orthogonal axis. In this configuration, attitude control is achieved by changing the speeds of each pair of the energy wheels 102 and 104, 106 and 108, and 110 and 112 (FIG. 1) in opposite directions. Such systems require six energy wheels 102 and 104, 106 and 108, and 110 and 112 (FIG. 1) (without redundancy) and when the wheels 102 and 104, 106 and 108, and 110 and 112 (FIG. 1) are storing energy, the speed of each pair is maintained at a constant difference. In order to provide redundancy, many designers have implemented a fourth pair of energy wheels. Another approach to the utilization of an energy wheel to provide both energy storage and attitude control of a spacecraft has been to double gimbal each of the energy wheels.
In another system, four energy wheels are combined in opposing pairs of which one pair of energy wheels is aligned orthogonally to the other pair of energy wheels.
However, while providing energy storage and attitude control, such a system does not provide redundancy. That is, if a single energy wheel is lost the other wheel in the pair must be shut down to produce an unbiased angular momentum in the spacecraft. In this configuration, the remaining pair of energy wheels produce zero net angular momentum, with both sets of gimbals in their null position. However, such a system has a singularity in the attitude control portion of the system at zero angular momentum. Further, there is no combination of gimbal rates that produces torque about the spin axis of the functioning pair of energy wheels.
What is needed is a minimum energy wheel configuration that can perform attitude control without singularities in the angular momentum from the gimbal angle Jacobian matrix at zero angular momentum.
The present invention is generally directed to a satellite energy and attitude control system that includes a first energy wheel, a second energy wheel and a third energy wheel. The first energy wheel is mounted in a first double gimbal and the second energy wheel is mounted in a second double gimbal. The third energy wheel is mounted in a third double gimbal and the first, second and third energy wheels, which have at least two degrees of motion orthogonal to their respective spin axes, are located within a single plane and positioned with respect to each other such that the total angular momentum provided by the first, second and third energy wheels sums to zero approximate an operational range center of the gimbals. According to another embodiment of the present invention, a fourth energy wheel is provided that is mounted in a fourth double gimbal and is located within the single plane. The fourth energy wheel is positioned with respect to the first, second and third energy wheels such that the total angular momentum provided by the first, second, third and fourth energy wheels sum to zero approximate an operational range of the gimbals.